The present invention generally relates to optoelectronic modules and, more particularly, to improved optoelectronic modules that can be efficiently and advantageously coupled to multimode optical fibers.
Fiber optic technology is playing an ever-increasing roll in the modern age of communications. As communication standards such as Fiber Channel (1062 Mbps) and Gigabit Ethernet (1000 Mbps) place ever-increasing demands on the physical layer infrastructure, optical fiber is being looked to more and more as the transmission medium of choice. Advancements in optoelectronic devices have furthered the desirability of optical fiber because optical fiber systems not only support the high data transmission rates, but the cost is becoming more and more affordable.
A key aspect to the affordability is the modularity by which the advancements in optical fiber technology are being implemented, particularly with regard to their backward compatibility with existing network components. Advancements that cannot be delivered to the marketplace with backward compatibility may not be as desirable as competing advancements which are backward compatible. For example, if an advancement requires recabling an entire building, then it may not be a viable solution. If an advancement requires specialized equipment, specialized connectors, specialized patch cords, etc., then it too may not be a viable solution. Accordingly, a desirable feature of any new technological advancement is the modularity and/or compatibility with existing components.
As an instance, it has been shown that the bandwidth of a multimode optical fiber can be increased by launching optical signals from a single-mode optical fiber into the multimode optical fiber with a deliberate, predetermined offset between the central axis of the single-mode optical fiber and the central axis of the multimode optical fiber. This feature, referred to as off-axis or offset launch condition, represents a significant advancement because it has the potential to extend the bandwidth of multimode optical fiber already installed in existing network configurations, such as in a local area network (LAN). By increasing the available bandwidth, the useful life of existing or new installations of multimode fiber may be lengthened.
However, because the dimensions of the offset for an offset launch condition are so small, typically less than 30 micrometers, the launching single-mode fiber and the receiving multimode optical fiber need to be precisely aligned, preferably within 4-8 micrometers (xcexcm). Two suggested methods for achieving this precise offset include the use of a specialized patch cord that incorporates a desired level of offset or an adapter that precisely aligns the optical fiber so that their cores have a predetermined offset, as described in the co-pending patent application Ser. Nos. 09/210,923 and 09/211,117, both of which are assigned to the assignee of the present application. While these techniques have some merit, they generally require one or more specialized components or pieces of equipment for effectuating an offset launch condition at the fiber interface.
Thus, there continues to exist an unsatisfied need in the industry for an optoelectronic module that can be coupled to a multimode optical fiber under an offset launch condition without utilizing specialized equipment or components.
The present invention is an optoelectronic module that can be coupled to a multimode optical fiber so as to achieve an offset launch condition without the use of specialized components or equipment. An optoelectronic module in accordance with the present invention achieves this by utilizing a single-mode optical fiber pigtail with an offset core. That is, the single-mode optical fiber pigtail includes a predetermined offset of the center of the core with respect to the center of the optical fiber. Such an offset can be readily manufactured in an optical fiber using rod-in-tube technology, or in a planar waveguide using standard photolithographic techniques. The precise offset can be designed to correspond to the offset launch zone of a multimode optical fiber to which the optoelectronic module is to be coupled. Accordingly, the available bandwidth of the multimode optical fiber may be increased.
In accordance with an aspect of the present invention, an optoelectronic module comprises an optoelectronic device, a single-mode optical conductor aligned with the optoelectronic device for receiving optical signals therefrom, wherein the single-mode optical conductor further includes a core surrounded by cladding. The center of the core is radially offset from the center of the cladding by a predetermined distance. The predetermined distance of the radial offset is sufficient to provide an offset launch condition when the optical conductor is coupled to a multimode optical fiber. The single-mode optical conductor may be an optical fiber or a planar optical waveguide. Further, the optoelectronic module may be a light transmitting device.
In the case where the single-mode optical conductor is an optical fiber, the center of the core may be offset from the center of the cladding by approximately 17-23 xcexcm for the single-mode optical fiber which is to be coupled with a multimode fiber having a core radius of approximately 31.25 xcexcm. Alternatively, where the core radius is approximately 25 xcexcm, the center of the core of the single-mode fiber is offset from the center of the cladding by approximately 10-16 xcexcm.
Further, the optoelectronic module may comprise a first multimode optical fiber coupled to the single-mode optical conductor, wherein the multimode optical fiber includes a core and a cladding surrounding the core. The center of the cladding of the first multimode optical fiber and the center of the cladding of the single-mode optical conductor are substantially coaxial, though the off-center core of the single-mode optical conductor provides for an offset launch condition into the multimode optical fiber.
In accordance with another aspect of the present invention, a method for fabricating an optoelectronic module comprises providing an optoelectronic transmitter device, providing a single-mode conductor having a first end, a second end, and a core surrounded by a cladding, and coupling the first end of a single mode optical conductor to the optoelectronic module so that the optical conductor receives optical signals from the optoelectronic module. The single-mode optical conductor is characterized by having the center of the core radially offset from the center of the cladding by a predetermined distance that is sufficient to provide an offset launch condition into a suitable multimode fiber which may be coupled to the second end of the single-mode optical conductor. The method further comprises the step of coupling such a multimode fiber to the second end of the single-mode optical conductor, wherein the predetermined offset produces the offset launch condition of optical signals transmitted from the single-mode optical fiber into the multimode optical fiber.
The step of providing the optical conductor may include the step of fabricating the optical conductor by inserting a silica-based core rod into a silica-based porous tube to form a fiber preform with a predetermined offset between the axial center of the core and the axial of the center of the porous tube. The single-mode optical conductor drawn from the preform will have the geometries of the fiber preform, including the predetermined offset, as well known in the art.
In accordance with another aspect of the present invention, a single-mode optical conductor, such as an optical fiber or waveguide, comprises a single-mode core region having a first central axis and a cladding region surrounding the core region and having a second central axis, wherein the first central axis is radially offset from the second central axis by a predetermined distance that is sufficient to provide an offset launch condition in a concentrically aligned and mating multimode optical conductor. The distance of the offset may be between 10-23 micrometers, depending on numerous factors, including but not limited to the radius of the core of the mating optical conductor and the bandwidth/distance requirement.
Other features and advantages of the present invention will become apparent to one skilled in the art upon examination of the following drawings and detailed description. It is intended that all such features and advantages be included herein within the scope of the present invention as defined by the appended claims.